Electronics systems, such as communication systems, radar systems, infrared-sensor systems, laser-tracking systems, or directed-energy systems, whether ground-based, mobile, airborne, shipboard, or spacecraft based, generally have several subsystems that receive power from a power source over an electric power buss. Certain subsystems may draw a ripple current from the power source that may affect the other subsystems. For example, in the case of certain types of sensor systems, a cryogenic cooler drive electronics system may draw 10 amps or more of ripple current at a nominal frequency between 35 and 100 Hz from the electric power buss. However, large ripple current draw may destabilize the buss and may degrade the performance of other electronics subsystems using the buss, particularly those managing low power sensor signals. Hence, the imposition of regulations with limitations for conducted emissions EMI such as MIL-STD-461.
Passive filters with large capacitors and inductors have been used to reduce the current ripple on an electric power buss. However, the size and weight of these large capacitors and inductors used for low frequency filter bandwidth make these approaches undesirable for applications where size and/or weight are factors that are considered. Shunt regulators in parallel with the load have also been used. These shunt regulators draw load current under light load conditions and reduce shunt power under system heavy load conditions, keeping the net current drawn from a power source somewhat constant. Although this approach may work well for relatively light fluctuating loads, it wastes power. At high power or for a large quantity of shunt regulators, the power dissipation of the shunt loads may become excessive, increasing net total power draw and reducing the efficiency of the power system. AC-coupled shunt regulators are also used, but they also suffer from excessive power dissipation, and because they are AC coupled, they suffer from bandwidth limitations.
In addition, motors can act as power sources in some operating conditions during some part of their operating cycle. Therefore, motor driver electronics may sink power from the motor as well as source power to the motor. For example, regenerative braking as used in some electric vehicles uses the drive motors as generators to provide regenerative braking. The amount of braking is proportional to the power drawn from the motor. For maximum efficiency, the power drawn from the motor to provide braking is recycled back to the vehicle battery.
Another example includes the above-mentioned cryogenic coolers. For some cryogenic coolers, the motors provide position control braking or temperature control by acting as a power source, absorbing energy from the fluid, and delivering electrical power, during some part of the operating cycle. The motor drive electronics of a cryogenic cooler system therefore not only sources power to the motor, but also sinks power from the motor.
Thus, in cryogenic cooler systems there is bidirectional power flow to and from the motors, and the motor drive electronics provides energy to the motors and receives energy from the motors during some part of the operating cycle. Historically, in cryogenic cooler systems, power sourced from some cryocooler motors has been simply dissipated in a resistor or other load and converted to heat. As a result, the electrical energy is not stored or converted to any other type of work and is therefore wasted. A small converter has been used in cryogenic cooler drive electronics to sink power from a motor and return power back to the source, for a motor that always sourced power. However, the use of a small converter for sinking power from a motor is only useful in cryogenic cooler systems in which a motor is always sourcing power.
Thus, there are needs to drive electric motors, and prevent ripple current from reflecting back to the electric power buss, i.e., there are general needs for systems and methods that efficiently control and regulate input current drawn from an electric power buss to reduce ripple current fed back to the electric power buss. In addition, there are needs to efficiently recycle motor power back to the input power source during those times when the motor is sourcing power. Also, there are needs for an efficient motor drive power system that provides both of these functions.